1. Field of the Invention
The present invention relates to a motor-driven vertical type injection molding apparatus in which a screw is vertically driven by a ball screw mechanism.
2. Related Background Art
FIG. 14 illustrates a known vertical driving mechansim for a screw in this type of motor-driven vertical type injection molding apparatus.
As depicted in FIG. 14, a ball screw 270 extending in the perpendicular direction is so provided in an upper base 273 serving as a molding apparatus body as to be unmovable in the axial direction but rotatable. Fixed to the upper end part of the ball screw 270 is a toothed pulley 276 to which a torque of an injection motor (not shown) is transferred. The ball screw 270 is rotated with rotation of the injection motor.
On the other hand, a screw (not shown) extending in the perpendicular direction is held at the lower portion of a screw holding member 258 so provided as to be incapable of rotating. A ball nut 275 screwed to the ball screw 270 is fixed to the upper part of the screw holding member 258.
Based on the construction described above, when the ball screw 270 is rotated by rotating the injection motor, the screw holding member 258 is driven upward and downward through the ball nut 275. On this occasion, when the screw holding member 258 is raised, the ball screw 270 protrudes below the ball nut 275. Hence, a relief portion 258b is formed under the ball nut 275 in the screw holding member 258 so that the ball screw 270 does not impinge on the screw holding member 258 even when the screw holding member 258 is raised.
The above-mentioned molding apparatus has an advantage that it is capable of being installed even in a narrow space because of a small installing area. But, since the molding apparatus has greater height than a horizontal type injection molding apparatus, the molding apparatus described above has a problem that it can not be installed in a low-ceilinged clean room or the like. Particularly, in the above-mentioned vertical driving mechanism for a screw, the ball screw is provided in the molding apparatus body, hence the screw holding member is provided with the ball nut and the relief portion of the ball screw. For this reason, the screw holding member has to increase in height corresponding to the ball nut and the relief portion. As a result, a height of the motor-driven vertical type injection molding apparatus increases.